It is well known to form bags from tubes, by closing ends of the tubes. Sometimes a tube is formed from a heat sealable material, and heat is used to form a seal that closes an end of the tube. As a contrasting example, sometimes the end of a tube is sewn closed to form a bag, such as when the tube is constructed of a material that is not heat sealable, or in other circumstances in which a suitable heat seal may not be formed (e.g., in tubes constructed of high strength packaging material). In some situations, a heat seal is considered superior to a sewn seal. Accordingly, it is desirable to provide improvements that promote the usage of heat seals (e.g., in some tubes constructed of high strength packaging material).